LECT. ii THE SOIL 29 



mould; others follow and run their course, and the 

 soil if not in a position to be washed away is gradually 

 deepened year by year. The mass thus formed 

 naturally will be dark in colour and soft in texture- 

 vegetable mould pure and simple. 



This alone is not sufficient to support useful crops, 

 for to use a common expression, there is not "bone 

 enough in it " ; but in due proportion soil so pro- 

 duced (organic) is of enormous value, and indeed 

 without it useful food crops could not be produced. 

 This accumulation of decayed vegetable matter is 

 known as " humus," and within certain limits the 

 greater the amount of this incorporated with soil of a 

 mineral origin, the greater is the fertility of the whole. 



Farmyard manure is good for land that does not 

 contain sufficient vegetable matter, because it supplies 

 humus, and yet plants and crops do not feed on this. 

 It is not food, but a producer of food and warmth. 

 Dark soils are warmer than those light in colour 

 because of the humus they contain, and land con- 

 taining a large proportion of vegetable matter does 

 not dry out in summer to nearly the same extent as 

 do soils that are comparatively destitute of it, because 

 humus has an affinity for moisture. 



Sandy soils, clayey soils, and marly soils are all 

 benefited by humus or material such as stable 

 manure and vegetable refuse that produce it ; but 

 black, soapy soils have enough or too much of such 

 matter, and need lime, with other mineral applica- 

 tions, to increase their fertility, as will be pointed 

 out subsequently. 



3. The Purpose Soil Serves. The main pur- 

 poses of the soil are two-fold. First to afford anchor- 

 age to the roots of trees and secure them in their 

 positions ; and secondly, to hold the requisite 

 materials for supporting growth. 



